1. Field of the Invention
The present invention relates to an optical scanner for use with laser printers and the like. More particularly, the invention relates to an optical scanner using lens optics for collimating the light from a light emitting source.
2. Description of the Related Art
Optical scanners are extensively used with optical printers, digital copiers and the like. The basic components of such optical sensors are: a light emitting source such as a semiconductor laser device; collimator lens optics with which the light beam issuing from the semiconductor laser device is collimated to parallel rays; cylindrical lens optics including a semi-cylindrical or cylindrical lens having different lens powers in sagittal and meridional directions; a deflector such as a polygonal mirror for deflecting the incident light in a direction corresponding to the main scanning direction; and an f.theta. lens as a scanning lens. The f.theta. lens has two functions, one for converging the deflected laser beam as a spot on a scanning surface such as a photoreceptor drum or belt, and one for moving the beam spot over the scanning surface at a substantially uniform speed.
As is well known, the light issued from semiconductor laser devices is divergent and, hence, in order to assure easy handling, the laser beam is often utilized after conversion to parallel rays by collimation with collimator lens optics.
Collimator lens optics are available in various types, such as a light source unit that performs collimation using a combined lens consisting of two or more spherical lens elements (see Japanese Patent Unexamined Publication No. Sho. 58-140713) and a light source unit that performs collimation using only one single aspheric lens element (see Japanese Patent Unexamined Publication No. Hei. 3-249720).
However, comprising collimator lens optics of two or more spherical lens elements has the disadvantage of the need to use an increased number of components. This results not only in complicated procedures of assembling, adjusting and other operations but also in a higher cost. If collimator lens optics is composed of one single aspheric lens element, the procedures of assembling, adjusting and other operations can be simplified but, on the other hand, aspheric lenses cannot be manufactured as easily and precisely as in the case of manufacturing spherical lenses by polishing or other mechanical methods; the method commonly used today is by molding glass but producing highly precise aspheric lenses consistently at low cost is difficult to realize by this method. Therefore, the optical scanner using collimator lens optics solely composed of one single aspheric lens is eventually costly.